1. Field of the Invention
The present invention relates generally to computer-aided design and, more specifically, to a method of power steering hose assembly design and analysis for a power steering system in a vehicle.
2. Description of the Related Art
A consumer's purchase decision regarding a product is influenced by both subjective and objective perceptions of the product. With respect to a product such as a vehicle, and in particular an automotive vehicle, the consumer perceives interior quietness as a desirable feature. To satisfy this consumer preference, it is advantageous for a vehicle designer to identify and minimize a potential source of noise, vibration or harshness (NVH) early in the design process.
A known source of noise within the interior of the vehicle is from a hydraulically-assisted power steering system. The power steering system includes a power steering pump that initiates a pressure ripple, which interacts with a hydraulic circuit and propagates throughout the power steering system as fluid-borne noise. Various noise reduction techniques are used to minimize the noise of the power steering system. For example, an attenuation device such as a flexible tuning cable is disposed within a power steering hose assembly, and in particular a high-pressure power steering hose assembly. The flexible tuning cable relies on a process of destructive interference to attenuate the pressure ripple. Through a series of reflections, the tuning cable induces a 180° phase difference in the pressure ripple, that ultimately reduces the amplitude of the pressure ripple. Advantageously, the length of the cable is adjustable to vary the attenuation ability of the tuning cable.
Another example of a noise reduction technique is structural damping, whereby the hose assembly length is increased so that any expansion of the hose wall assists in absorbing the energy from the pressure ripple. In addition, the hose reduces the wave speed in the fluid, thus shortening the pressure ripple wavelength and increasing the effectiveness of the tuning cable.
While these noise reduction techniques work well, it is advantageous to predict the NVH characteristics of the power steering system, and the effectiveness of a noise reduction technique, early in the design process. In the past, the NVH characteristics of the power steering system, and in particular the power steering hose assembly were predicted using a combination of analytical, empirical, or experimental methodologies. An example of an experimental methodology is trial and error using a physical model. However, this methodology type is time consuming and costly. An example of an analytical methodology is a model of the power steering system represented by a set of equations resulting in a closed form solution. A closed form solution is an exact answer to a given set of equations. However, as power steering system models become increasingly complex, due to the nonlinear nature of the system, the complexity of the solution also increases. Therefore, analytical tools are not easy to use and are frequently constrained to analysis of simplified geometry and material properties. Thus, there is a need in the art for a method of power steering system hose assembly design and analysis that accurately and rapidly assesses the NVH characteristics of the system, including transfer loss, fluid flow characteristics, system vibration, and airborne noise prediction.